In some conventional communications systems, a frequency divider may be utilized to downconvert a signal to a lower frequency. In one application, for example, a frequency divider may be part of a phase-locked loop (PLL), which generates an output signal of a desired frequency utilizing a voltage controlled oscillator (VCO). The VCO may generate a signal whose frequency depends on a control voltage generated by a phase detector. The phase detector may generate the control voltage by comparing a reference signal to a feedback portion of the VCO output signal. In this manner, the VCO output signal may be kept from drifting to a different frequency value.
The reference signal, however, may have a lower frequency than the VCO output signal, since if the reference signal were the same frequency or a higher frequency as the desired VCO output signal, there would be no need for the PLL. The PLL may use a frequency divider so that the VCO output signal frequency is a multiple of the reference signal frequency. To make the PLL more versatile, a processor may control the frequency divider to allow it to divide the VCO output signal by different values. This may effectively allow the VCO to output signals whose frequencies may be various multiples of the reference signal.
Therefore, the PLL may be utilized by various transmitters and receivers that need to be able to transmit or receive a plurality of frequencies. Some devices which may need to do this may be, for example, AM and FM radios, television sets, walkie-talkies, cordless phones, and wireless phones, whether for cellular or personal communication service (PCS) system. However, as the carrier frequency increases, the circuitry that handles the radio frequency (RF) signals must be adapted to handle the higher frequencies. With wireless systems, for example, the PCS system, the RF carrier may have a frequency of a gigahertz or more. One problem with existing frequency divider circuits is that they have to operate over a wide range of carrier frequencies. As a result, a different frequency divider circuit has to be utilized for applications operating at different frequencies. For devices operating over a wider frequency range, a plurality of frequency dividers are required and this significantly increases system cost.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.